Overview of HIV and the immune system

The immune system is gradually disrupted. HIV kills cells in the lymph nodes (small glands filled with immune cells that trap foreign organisms) and in other sites. This throws the immune system out of balance.
Virus levels in the blood and the lymph nodes increase because the immune system cannot keep up with the amount of virus constantly produced.
HIV constantly changes itself, avoiding attack by the antibodies and immune cells that normally control infections.
Each generation of viruses is slightly different. This constant evolution helps HIV keep one step ahead of the immune system. Immune cells can only look for viruses that resemble the previous generation of HIV, so the virus constantly ‘escapes’ the immune system.
CD4 T-cells gradually decline in number. This is because they are killed by HIV and also because they are over-activated and this leads to increased T-cell death.
HIV destroys memory CD4 T-cells that have been primed to rapidly respond to infections. This is why opportunistic infections such as Pneumocystis pneumonia (PCP) and Candida (thrush) develop when the CD4 cell count falls.

The level of virus in the blood and the CD4 cell count can predict the risk of developing AIDS.
Without treatment of any sort, at least 50% of people infected with HIV will develop AIDS within ten years.
In the last few years, substantial improvements in treatment have slowed progression of HIV disease and reduced the risk of developing AIDS.
The greater the effect of drugs on virus levels in the body, the lower the risk of progressing to a diagnosis of AIDS.
Specific co-factors may influence the speed at which HIV disease develops.
Inherited genetic factors may accelerate or slow the speed at which HIV disease develops.
Disease progression is also related to the doctor's experience level. Generally, patients have the best clinical outcomes when they are treated by experienced HIV care providers.
A small proportion of people infected with HIV show few signs of immune system damage, even after being infected for more than ten years. These individuals are called long-term non-progressors and researchers have been looking into genetic or biological causes to explain this phenomenon.